Fiber optic cables are used to transmit light in fiber-optic communications and optical sensing. For example, in optical sensing, light can represent various signal types, such as temperature, pressure, strain, acceleration, and the like. In some applications, optical sensing can be used in a wellbore by communicating light between a source and downhole sensors or actuators (or both). The fiber optic cables can be embedded in the wellbore's casing, or run down into the wellbore with a well tool (e.g., a logging tool string in a drill pipe string). To cover long distances in a wellbore or in other applications, two or more lengths of fiber optic cables are often joined or coupled using a coupling part. Back reflection can result from, among other things, misalignment of the coupling in the coupling part.
Like reference symbols in the various drawings indicate like elements.